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<li class="navelem"><a class="el" href="../../d9/df8/tutorial_root.html">OpenCV Tutorials</a></li><li class="navelem"><a class="el" href="../../d9/d97/tutorial_table_of_content_features2d.html">2D Features framework (feature2d module)</a></li>  </ul>
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<div class="title">Creating your own corner detector </div>  </div>
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<div class="textblock"><p><b>Prev Tutorial:</b> <a class="el" href="../../d8/dd8/tutorial_good_features_to_track.html">Shi-Tomasi corner detector</a></p>
<p><b>Next Tutorial:</b> <a class="el" href="../../dd/d92/tutorial_corner_subpixels.html">Detecting corners location in subpixels</a></p>
<table class="doxtable">
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<th align="right"></th><th align="left"></th></tr>
<tr>
<td align="right">Original author </td><td align="left">Ana Huamán </td></tr>
<tr>
<td align="right">Compatibility </td><td align="left">OpenCV &gt;= 3.0 </td></tr>
</table>
<h2>Goal </h2>
<p>In this tutorial you will learn how to:</p>
<ul>
<li>Use the OpenCV function <a class="el" href="../../dd/d1a/group__imgproc__feature.html#ga4055896d9ef77dd3cacf2c5f60e13f1c">cv::cornerEigenValsAndVecs</a> to find the eigenvalues and eigenvectors to determine if a pixel is a corner.</li>
<li>Use the OpenCV function <a class="el" href="../../dd/d1a/group__imgproc__feature.html#ga3dbce297c1feb859ee36707e1003e0a8">cv::cornerMinEigenVal</a> to find the minimum eigenvalues for corner detection.</li>
<li>Implement our own version of the Harris detector as well as the Shi-Tomasi detector, by using the two functions above.</li>
</ul>
<h2>Theory </h2>
<h2>Code </h2>
 <div class='newInnerHTML' title='cpp' style='display: none;'>C++</div><div class='toggleable_div label_cpp' style='display: none;'><p> This tutorial code's is shown lines below. You can also download it from <a href="https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/TrackingMotion/cornerDetector_Demo.cpp">here</a></p>
<div class="fragment"><div class="line"></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"><span class="keyword">using namespace </span>std;</div><div class="line"></div><div class="line"><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> src, src_gray;</div><div class="line"><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> myHarris_dst, myHarris_copy, Mc;</div><div class="line"><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> myShiTomasi_dst, myShiTomasi_copy;</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> myShiTomasi_qualityLevel = 50;</div><div class="line"><span class="keywordtype">int</span> myHarris_qualityLevel = 50;</div><div class="line"><span class="keywordtype">int</span> max_qualityLevel = 100;</div><div class="line"></div><div class="line"><span class="keywordtype">double</span> myHarris_minVal, myHarris_maxVal;</div><div class="line"><span class="keywordtype">double</span> myShiTomasi_minVal, myShiTomasi_maxVal;</div><div class="line"></div><div class="line"><a class="code" href="../../d1/dd6/classcv_1_1RNG.html">RNG</a> rng(12345);</div><div class="line"></div><div class="line"><span class="keyword">const</span> <span class="keywordtype">char</span>* myHarris_window = <span class="stringliteral">&quot;My Harris corner detector&quot;</span>;</div><div class="line"><span class="keyword">const</span> <span class="keywordtype">char</span>* myShiTomasi_window = <span class="stringliteral">&quot;My Shi Tomasi corner detector&quot;</span>;</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> myShiTomasi_function( <span class="keywordtype">int</span>, <span class="keywordtype">void</span>* );</div><div class="line"><span class="keywordtype">void</span> myHarris_function( <span class="keywordtype">int</span>, <span class="keywordtype">void</span>* );</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main( <span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv )</div><div class="line">{</div><div class="line">    <a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">CommandLineParser</a> parser( argc, argv, <span class="stringliteral">&quot;{@input | building.jpg | input image}&quot;</span> );</div><div class="line">    src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( <a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>( parser.get&lt;<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>&gt;( <span class="stringliteral">&quot;@input&quot;</span> ) ) );</div><div class="line">    <span class="keywordflow">if</span> ( src.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abbec3525a852e77998aba034813fded4">empty</a>() )</div><div class="line">    {</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Could not open or find the image!\n&quot;</span> &lt;&lt; endl;</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Usage: &quot;</span> &lt;&lt; argv[0] &lt;&lt; <span class="stringliteral">&quot; &lt;Input image&gt;&quot;</span> &lt;&lt; endl;</div><div class="line">        <span class="keywordflow">return</span> -1;</div><div class="line">    }</div><div class="line">    <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>( src, src_gray, <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a353a4b8db9040165db4dacb5bcefb6ea">COLOR_BGR2GRAY</a> );</div><div class="line"></div><div class="line">    <span class="keywordtype">int</span> blockSize = 3, apertureSize = 3;</div><div class="line"></div><div class="line">    <a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga4055896d9ef77dd3cacf2c5f60e13f1c">cornerEigenValsAndVecs</a>( src_gray, myHarris_dst, blockSize, apertureSize );</div><div class="line"></div><div class="line">    <span class="comment">/* calculate Mc */</span></div><div class="line">    Mc = <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>( src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#a146f8e8dda07d1365a575ab83d9828d1">size</a>(), <a class="code" href="../../d1/d1b/group__core__hal__interface.html#ga32ec76240e43e4c9c7b2e2785180a7e6">CV_32FC1</a> );</div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">int</span> i = 0; i &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>; i++ )</div><div class="line">    {</div><div class="line">        <span class="keywordflow">for</span>( <span class="keywordtype">int</span> j = 0; j &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a>; j++ )</div><div class="line">        {</div><div class="line">            <span class="keywordtype">float</span> lambda_1 = myHarris_dst.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<a class="code" href="../../d6/dcf/classcv_1_1Vec.html">Vec6f</a>&gt;(i, j)[0];</div><div class="line">            <span class="keywordtype">float</span> lambda_2 = myHarris_dst.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<a class="code" href="../../d6/dcf/classcv_1_1Vec.html">Vec6f</a>&gt;(i, j)[1];</div><div class="line">            Mc.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">float</span>&gt;(i, j) = lambda_1*lambda_2 - 0.04f*<a class="code" href="../../d7/dcc/group__core__utils__softfloat.html#ga8bc36646a43b82baa15f151a973fb0c5">pow</a>( ( lambda_1 + lambda_2 ), 2 );</div><div class="line">        }</div><div class="line">    }</div><div class="line"></div><div class="line">    <a class="code" href="../../d2/de8/group__core__array.html#gab473bf2eb6d14ff97e89b355dac20707">minMaxLoc</a>( Mc, &amp;myHarris_minVal, &amp;myHarris_maxVal );</div><div class="line"></div><div class="line">    <span class="comment">/* Create Window and Trackbar */</span></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>( myHarris_window );</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">createTrackbar</a>( <span class="stringliteral">&quot;Quality Level:&quot;</span>, myHarris_window, &amp;myHarris_qualityLevel, max_qualityLevel, myHarris_function );</div><div class="line">    myHarris_function( 0, 0 );</div><div class="line"></div><div class="line">    <a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga3dbce297c1feb859ee36707e1003e0a8">cornerMinEigenVal</a>( src_gray, myShiTomasi_dst, blockSize, apertureSize );</div><div class="line"></div><div class="line">    <a class="code" href="../../d2/de8/group__core__array.html#gab473bf2eb6d14ff97e89b355dac20707">minMaxLoc</a>( myShiTomasi_dst, &amp;myShiTomasi_minVal, &amp;myShiTomasi_maxVal );</div><div class="line"></div><div class="line">    <span class="comment">/* Create Window and Trackbar */</span></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">namedWindow</a>( myShiTomasi_window );</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">createTrackbar</a>( <span class="stringliteral">&quot;Quality Level:&quot;</span>, myShiTomasi_window, &amp;myShiTomasi_qualityLevel, max_qualityLevel, myShiTomasi_function );</div><div class="line">    myShiTomasi_function( 0, 0 );</div><div class="line"></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> myShiTomasi_function( <span class="keywordtype">int</span>, <span class="keywordtype">void</span>* )</div><div class="line">{</div><div class="line">    myShiTomasi_copy = src.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#adff2ea98da45eae0833e73582dd4a660">clone</a>();</div><div class="line">    myShiTomasi_qualityLevel = <a class="code" href="../../db/de0/group__core__utils.html#gafa99ec4acc4ecb2dc3c2d05da15d0e3f">MAX</a>(myShiTomasi_qualityLevel, 1);</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">int</span> i = 0; i &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>; i++ )</div><div class="line">    {</div><div class="line">        <span class="keywordflow">for</span>( <span class="keywordtype">int</span> j = 0; j &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a>; j++ )</div><div class="line">        {</div><div class="line">            <span class="keywordflow">if</span>( myShiTomasi_dst.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">float</span>&gt;(i,j) &gt; myShiTomasi_minVal + ( myShiTomasi_maxVal - myShiTomasi_minVal )*myShiTomasi_qualityLevel/max_qualityLevel )</div><div class="line">            {</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#gaf10604b069374903dbd0f0488cb43670">circle</a>( myShiTomasi_copy, <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(j,i), 4, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>( rng.uniform(0,256), rng.uniform(0,256), rng.uniform(0,256) ), <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a89c5f6beef080e6df347167f85e07b9e">FILLED</a> );</div><div class="line">            }</div><div class="line">        }</div><div class="line">    }</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( myShiTomasi_window, myShiTomasi_copy );</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> myHarris_function( <span class="keywordtype">int</span>, <span class="keywordtype">void</span>* )</div><div class="line">{</div><div class="line">    myHarris_copy = src.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#adff2ea98da45eae0833e73582dd4a660">clone</a>();</div><div class="line">    myHarris_qualityLevel = <a class="code" href="../../db/de0/group__core__utils.html#gafa99ec4acc4ecb2dc3c2d05da15d0e3f">MAX</a>(myHarris_qualityLevel, 1);</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">int</span> i = 0; i &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>; i++ )</div><div class="line">    {</div><div class="line">        <span class="keywordflow">for</span>( <span class="keywordtype">int</span> j = 0; j &lt; src_gray.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa3e5a47585c9ef6a0842556739155e3e">cols</a>; j++ )</div><div class="line">        {</div><div class="line">            <span class="keywordflow">if</span>( Mc.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">float</span>&gt;(i,j) &gt; myHarris_minVal + ( myHarris_maxVal - myHarris_minVal )*myHarris_qualityLevel/max_qualityLevel )</div><div class="line">            {</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#gaf10604b069374903dbd0f0488cb43670">circle</a>( myHarris_copy, <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(j,i), 4, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>( rng.uniform(0,256), rng.uniform(0,256), rng.uniform(0,256) ), <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a89c5f6beef080e6df347167f85e07b9e">FILLED</a> );</div><div class="line">            }</div><div class="line">        }</div><div class="line">    }</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>( myHarris_window, myHarris_copy );</div><div class="line">}</div></div><!-- fragment -->  </div>  <div class='newInnerHTML' title='java' style='display: none;'>Java</div><div class='toggleable_div label_java' style='display: none;'><p> This tutorial code's is shown lines below. You can also download it from <a href="https://github.com/opencv/opencv/tree/master/samples/java/tutorial_code/TrackingMotion/generic_corner_detector/CornerDetectorDemo.java">here</a></p>
<div class="fragment"><div class="line"><span class="keyword">import</span> java.awt.BorderLayout;</div><div class="line"><span class="keyword">import</span> java.awt.Container;</div><div class="line"><span class="keyword">import</span> java.awt.Image;</div><div class="line"><span class="keyword">import</span> java.util.Random;</div><div class="line"></div><div class="line"><span class="keyword">import</span> javax.swing.BoxLayout;</div><div class="line"><span class="keyword">import</span> javax.swing.ImageIcon;</div><div class="line"><span class="keyword">import</span> javax.swing.JFrame;</div><div class="line"><span class="keyword">import</span> javax.swing.JLabel;</div><div class="line"><span class="keyword">import</span> javax.swing.JPanel;</div><div class="line"><span class="keyword">import</span> javax.swing.JSlider;</div><div class="line"><span class="keyword">import</span> javax.swing.event.ChangeEvent;</div><div class="line"><span class="keyword">import</span> javax.swing.event.ChangeListener;</div><div class="line"></div><div class="line"><span class="keyword">import</span> org.opencv.core.Core;</div><div class="line"><span class="keyword">import</span> org.opencv.core.Core.MinMaxLocResult;</div><div class="line"><span class="keyword">import</span> org.opencv.core.CvType;</div><div class="line"><span class="keyword">import</span> org.opencv.core.Mat;</div><div class="line"><span class="keyword">import</span> org.opencv.core.Point;</div><div class="line"><span class="keyword">import</span> org.opencv.core.Scalar;</div><div class="line"><span class="keyword">import</span> org.opencv.highgui.HighGui;</div><div class="line"><span class="keyword">import</span> org.opencv.imgcodecs.Imgcodecs;</div><div class="line"><span class="keyword">import</span> org.opencv.imgproc.Imgproc;</div><div class="line"></div><div class="line"><span class="keyword">class </span>CornerDetector {</div><div class="line">    <span class="keyword">private</span> Mat src = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat srcGray = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat harrisDst = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat shiTomasiDst = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat harrisCopy = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat shiTomasiCopy = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> Mat Mc = <span class="keyword">new</span> Mat();</div><div class="line">    <span class="keyword">private</span> JFrame frame;</div><div class="line">    <span class="keyword">private</span> JLabel harrisImgLabel;</div><div class="line">    <span class="keyword">private</span> JLabel shiTomasiImgLabel;</div><div class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keywordtype">int</span> MAX_QUALITY_LEVEL = 100;</div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">int</span> qualityLevel = 50;</div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">double</span> harrisMinVal;</div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">double</span> harrisMaxVal;</div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">double</span> shiTomasiMinVal;</div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">double</span> shiTomasiMaxVal;</div><div class="line">    <span class="keyword">private</span> Random rng = <span class="keyword">new</span> Random(12345);</div><div class="line"></div><div class="line">    <span class="keyword">public</span> CornerDetector(<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>[] args) {</div><div class="line">        <a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a> filename = args.length &gt; 0 ? args[0] : <span class="stringliteral">&quot;../data/building.jpg&quot;</span>;</div><div class="line">        src = Imgcodecs.imread(filename);</div><div class="line">        <span class="keywordflow">if</span> (src.empty()) {</div><div class="line">            System.err.println(<span class="stringliteral">&quot;Cannot read image: &quot;</span> + filename);</div><div class="line">            System.exit(0);</div><div class="line">        }</div><div class="line"></div><div class="line">        Imgproc.cvtColor(src, srcGray, Imgproc.COLOR_BGR2GRAY);</div><div class="line"></div><div class="line">        <span class="comment">// Create and set up the window.</span></div><div class="line">        frame = <span class="keyword">new</span> JFrame(<span class="stringliteral">&quot;Creating your own corner detector demo&quot;</span>);</div><div class="line">        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);</div><div class="line">        <span class="comment">// Set up the content pane.</span></div><div class="line">        Image img = HighGui.toBufferedImage(src);</div><div class="line">        addComponentsToPane(frame.getContentPane(), img);</div><div class="line">        <span class="comment">// Use the content pane&#39;s default BorderLayout. No need for</span></div><div class="line">        <span class="comment">// setLayout(new BorderLayout());</span></div><div class="line">        <span class="comment">// Display the window.</span></div><div class="line">        frame.pack();</div><div class="line">        frame.setVisible(<span class="keyword">true</span>);</div><div class="line"></div><div class="line">        <span class="keywordtype">int</span> blockSize = 3, apertureSize = 3;</div><div class="line"></div><div class="line">        Imgproc.cornerEigenValsAndVecs(srcGray, harrisDst, blockSize, apertureSize);</div><div class="line"></div><div class="line">        <span class="comment">/* calculate Mc */</span></div><div class="line">        Mc = Mat.zeros(srcGray.size(), CvType.CV_32F);</div><div class="line"></div><div class="line">        <span class="keywordtype">float</span>[] harrisData = <span class="keyword">new</span> <span class="keywordtype">float</span>[(int) (harrisDst.total() * harrisDst.channels())];</div><div class="line">        harrisDst.get(0, 0, harrisData);</div><div class="line">        <span class="keywordtype">float</span>[] McData = <span class="keyword">new</span> <span class="keywordtype">float</span>[(int) (Mc.total() * Mc.channels())];</div><div class="line">        Mc.get(0, 0, McData);</div><div class="line"></div><div class="line">        <span class="keywordflow">for</span>( <span class="keywordtype">int</span> i = 0; i &lt; srcGray.rows(); i++ ) {</div><div class="line">            <span class="keywordflow">for</span>( <span class="keywordtype">int</span> j = 0; j &lt; srcGray.cols(); j++ ) {</div><div class="line">                <span class="keywordtype">float</span> lambda1 = harrisData[(i*srcGray.cols() + j) * 6];</div><div class="line">                <span class="keywordtype">float</span> lambda2 = harrisData[(i*srcGray.cols() + j) * 6 + 1];</div><div class="line">                McData[i*srcGray.cols()+j] = (float) (lambda1*lambda2 - 0.04f*Math.pow( ( lambda1 + lambda2 ), 2 ));</div><div class="line">            }</div><div class="line">        }</div><div class="line">        Mc.put(0, 0, McData);</div><div class="line"></div><div class="line">        MinMaxLocResult res = Core.minMaxLoc(Mc);</div><div class="line">        harrisMinVal = res.minVal;</div><div class="line">        harrisMaxVal = res.maxVal;</div><div class="line"></div><div class="line">        Imgproc.cornerMinEigenVal(srcGray, shiTomasiDst, blockSize, apertureSize);</div><div class="line">        res = Core.minMaxLoc(shiTomasiDst);</div><div class="line">        shiTomasiMinVal = res.minVal;</div><div class="line">        shiTomasiMaxVal = res.maxVal;</div><div class="line"></div><div class="line">        update();</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">void</span> addComponentsToPane(Container pane, Image img) {</div><div class="line">        <span class="keywordflow">if</span> (!(pane.getLayout() instanceof BorderLayout)) {</div><div class="line">            pane.add(<span class="keyword">new</span> JLabel(<span class="stringliteral">&quot;Container doesn&#39;t use BorderLayout!&quot;</span>));</div><div class="line">            <span class="keywordflow">return</span>;</div><div class="line">        }</div><div class="line"></div><div class="line">        JPanel sliderPanel = <span class="keyword">new</span> JPanel();</div><div class="line">        sliderPanel.setLayout(<span class="keyword">new</span> BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));</div><div class="line"></div><div class="line">        sliderPanel.add(<span class="keyword">new</span> JLabel(<span class="stringliteral">&quot;Max  corners:&quot;</span>));</div><div class="line">        JSlider slider = <span class="keyword">new</span> JSlider(0, MAX_QUALITY_LEVEL, qualityLevel);</div><div class="line">        slider.setMajorTickSpacing(20);</div><div class="line">        slider.setMinorTickSpacing(10);</div><div class="line">        slider.setPaintTicks(<span class="keyword">true</span>);</div><div class="line">        slider.setPaintLabels(<span class="keyword">true</span>);</div><div class="line">        slider.addChangeListener(<span class="keyword">new</span> ChangeListener() {</div><div class="line">            @Override</div><div class="line">            <span class="keyword">public</span> <span class="keywordtype">void</span> stateChanged(ChangeEvent e) {</div><div class="line">                JSlider source = (JSlider) e.getSource();</div><div class="line">                qualityLevel = source.getValue();</div><div class="line">                update();</div><div class="line">            }</div><div class="line">        });</div><div class="line">        sliderPanel.add(slider);</div><div class="line">        pane.add(sliderPanel, BorderLayout.PAGE_START);</div><div class="line"></div><div class="line">        JPanel imgPanel = <span class="keyword">new</span> JPanel();</div><div class="line">        harrisImgLabel = <span class="keyword">new</span> JLabel(<span class="keyword">new</span> ImageIcon(img));</div><div class="line">        shiTomasiImgLabel = <span class="keyword">new</span> JLabel(<span class="keyword">new</span> ImageIcon(img));</div><div class="line">        imgPanel.add(harrisImgLabel);</div><div class="line">        imgPanel.add(shiTomasiImgLabel);</div><div class="line">        pane.add(imgPanel, BorderLayout.CENTER);</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="keyword">private</span> <span class="keywordtype">void</span> update() {</div><div class="line">        <span class="keywordtype">int</span> qualityLevelVal = Math.max(qualityLevel, 1);</div><div class="line"></div><div class="line">        <span class="comment">//Harris</span></div><div class="line">        harrisCopy = src.clone();</div><div class="line"></div><div class="line">        <span class="keywordtype">float</span>[] McData = <span class="keyword">new</span> <span class="keywordtype">float</span>[(int) (Mc.total() * Mc.channels())];</div><div class="line">        Mc.get(0, 0, McData);</div><div class="line">        <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; srcGray.rows(); i++) {</div><div class="line">            <span class="keywordflow">for</span> (<span class="keywordtype">int</span> j = 0; j &lt; srcGray.cols(); j++) {</div><div class="line">                <span class="keywordflow">if</span> (McData[i * srcGray.cols() + j] &gt; harrisMinVal</div><div class="line">                        + (harrisMaxVal - harrisMinVal) * qualityLevelVal / MAX_QUALITY_LEVEL) {</div><div class="line">                    Imgproc.circle(harrisCopy, <span class="keyword">new</span> <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(j, i), 4,</div><div class="line">                            <span class="keyword">new</span> <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(rng.nextInt(256), rng.nextInt(256), rng.nextInt(256)), Imgproc.FILLED);</div><div class="line">                }</div><div class="line">            }</div><div class="line">        }</div><div class="line"></div><div class="line">        <span class="comment">//Shi-Tomasi</span></div><div class="line">        shiTomasiCopy = src.clone();</div><div class="line"></div><div class="line">        <span class="keywordtype">float</span>[] shiTomasiData = <span class="keyword">new</span> <span class="keywordtype">float</span>[(int) (shiTomasiDst.total() * shiTomasiDst.channels())];</div><div class="line">        shiTomasiDst.get(0, 0, shiTomasiData);</div><div class="line">        <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; srcGray.rows(); i++) {</div><div class="line">            <span class="keywordflow">for</span> (<span class="keywordtype">int</span> j = 0; j &lt; srcGray.cols(); j++) {</div><div class="line">                <span class="keywordflow">if</span> (shiTomasiData[i * srcGray.cols() + j] &gt; shiTomasiMinVal</div><div class="line">                        + (shiTomasiMaxVal - shiTomasiMinVal) * qualityLevelVal / MAX_QUALITY_LEVEL) {</div><div class="line">                    Imgproc.circle(shiTomasiCopy, <span class="keyword">new</span> <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(j, i), 4,</div><div class="line">                            <span class="keyword">new</span> <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(rng.nextInt(256), rng.nextInt(256), rng.nextInt(256)), Imgproc.FILLED);</div><div class="line">                }</div><div class="line">            }</div><div class="line">        }</div><div class="line"></div><div class="line">        harrisImgLabel.setIcon(<span class="keyword">new</span> ImageIcon(HighGui.toBufferedImage(harrisCopy)));</div><div class="line">        shiTomasiImgLabel.setIcon(<span class="keyword">new</span> ImageIcon(HighGui.toBufferedImage(shiTomasiCopy)));</div><div class="line">        frame.repaint();</div><div class="line">    }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">public</span> <span class="keyword">class </span>CornerDetectorDemo {</div><div class="line">    <span class="keyword">public</span> <span class="keyword">static</span> <span class="keywordtype">void</span> main(<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>[] args) {</div><div class="line">        <span class="comment">// Load the native OpenCV library</span></div><div class="line">        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);</div><div class="line"></div><div class="line">        <span class="comment">// Schedule a job for the event dispatch thread:</span></div><div class="line">        <span class="comment">// creating and showing this application&#39;s GUI.</span></div><div class="line">        javax.swing.SwingUtilities.invokeLater(<span class="keyword">new</span> Runnable() {</div><div class="line">            @Override</div><div class="line">            <span class="keyword">public</span> <span class="keywordtype">void</span> run() {</div><div class="line">                <span class="keyword">new</span> CornerDetector(args);</div><div class="line">            }</div><div class="line">        });</div><div class="line">    }</div><div class="line">}</div></div><!-- fragment -->  </div>  <div class='newInnerHTML' title='python' style='display: none;'>Python</div><div class='toggleable_div label_python' style='display: none;'><p> This tutorial code's is shown lines below. You can also download it from <a href="https://github.com/opencv/opencv/tree/master/samples/python/tutorial_code/TrackingMotion/generic_corner_detector/cornerDetector_Demo.py">here</a></p>
<div class="fragment"><div class="line"><span class="keyword">from</span> __future__ <span class="keyword">import</span> print_function</div><div class="line"><span class="keyword">import</span> cv2 <span class="keyword">as</span> cv</div><div class="line"><span class="keyword">import</span> numpy <span class="keyword">as</span> np</div><div class="line"><span class="keyword">import</span> argparse</div><div class="line"><span class="keyword">import</span> random <span class="keyword">as</span> rng</div><div class="line"></div><div class="line">myHarris_window = <span class="stringliteral">&#39;My Harris corner detector&#39;</span></div><div class="line">myShiTomasi_window = <span class="stringliteral">&#39;My Shi Tomasi corner detector&#39;</span></div><div class="line">myHarris_qualityLevel = 50</div><div class="line">myShiTomasi_qualityLevel = 50</div><div class="line">max_qualityLevel = 100</div><div class="line">rng.seed(12345)</div><div class="line"></div><div class="line"><span class="keyword">def </span>myHarris_function(val):</div><div class="line">    myHarris_copy = np.copy(src)</div><div class="line">    myHarris_qualityLevel = <a class="code" href="../../d1/d10/classcv_1_1MatExpr.html#a6dff8b6e9105b6d817b493e7be157c90">max</a>(val, 1)</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span> i <span class="keywordflow">in</span> range(src_gray.shape[0]):</div><div class="line">        <span class="keywordflow">for</span> j <span class="keywordflow">in</span> range(src_gray.shape[1]):</div><div class="line">            <span class="keywordflow">if</span> Mc[i,j] &gt; myHarris_minVal + ( myHarris_maxVal - myHarris_minVal )*myHarris_qualityLevel/max_qualityLevel:</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#gaf10604b069374903dbd0f0488cb43670">cv.circle</a>(myHarris_copy, (j,i), 4, (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256)), cv.FILLED)</div><div class="line"></div><div class="line">    <a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(myHarris_window, myHarris_copy)</div><div class="line"></div><div class="line"><span class="keyword">def </span>myShiTomasi_function(val):</div><div class="line">    myShiTomasi_copy = np.copy(src)</div><div class="line">    myShiTomasi_qualityLevel = <a class="code" href="../../d1/d10/classcv_1_1MatExpr.html#a6dff8b6e9105b6d817b493e7be157c90">max</a>(val, 1)</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span> i <span class="keywordflow">in</span> range(src_gray.shape[0]):</div><div class="line">        <span class="keywordflow">for</span> j <span class="keywordflow">in</span> range(src_gray.shape[1]):</div><div class="line">            <span class="keywordflow">if</span> myShiTomasi_dst[i,j] &gt; myShiTomasi_minVal + ( myShiTomasi_maxVal - myShiTomasi_minVal )*myShiTomasi_qualityLevel/max_qualityLevel:</div><div class="line">                <a class="code" href="../../d6/d6e/group__imgproc__draw.html#gaf10604b069374903dbd0f0488cb43670">cv.circle</a>(myShiTomasi_copy, (j,i), 4, (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256)), cv.FILLED)</div><div class="line"></div><div class="line">    <a class="code" href="../../df/d24/group__highgui__opengl.html#gaae7e90aa3415c68dba22a5ff2cefc25d">cv.imshow</a>(myShiTomasi_window, myShiTomasi_copy)</div><div class="line"></div><div class="line"><span class="comment"># Load source image and convert it to gray</span></div><div class="line">parser = argparse.ArgumentParser(description=<span class="stringliteral">&#39;Code for Creating your own corner detector tutorial.&#39;</span>)</div><div class="line">parser.add_argument(<span class="stringliteral">&#39;--input&#39;</span>, help=<span class="stringliteral">&#39;Path to input image.&#39;</span>, default=<span class="stringliteral">&#39;building.jpg&#39;</span>)</div><div class="line">args = parser.parse_args()</div><div class="line"></div><div class="line">src = <a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">cv.imread</a>(<a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">cv.samples.findFile</a>(args.input))</div><div class="line"><span class="keywordflow">if</span> src <span class="keywordflow">is</span> <span class="keywordtype">None</span>:</div><div class="line">    <a class="code" href="../../df/d57/namespacecv_1_1dnn.html#a701210a0203f2786cbfd04b2bd56da47">print</a>(<span class="stringliteral">&#39;Could not open or find the image:&#39;</span>, args.input)</div><div class="line">    exit(0)</div><div class="line"></div><div class="line">src_gray = <a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cv.cvtColor</a>(src, cv.COLOR_BGR2GRAY)</div><div class="line"></div><div class="line"><span class="comment"># Set some parameters</span></div><div class="line">blockSize = 3</div><div class="line">apertureSize = 3</div><div class="line"></div><div class="line"><span class="comment"># My Harris matrix -- Using cornerEigenValsAndVecs</span></div><div class="line">myHarris_dst = <a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga4055896d9ef77dd3cacf2c5f60e13f1c">cv.cornerEigenValsAndVecs</a>(src_gray, blockSize, apertureSize)</div><div class="line"></div><div class="line"><span class="comment"># calculate Mc</span></div><div class="line">Mc = np.empty(src_gray.shape, dtype=np.float32)</div><div class="line"><span class="keywordflow">for</span> i <span class="keywordflow">in</span> range(src_gray.shape[0]):</div><div class="line">    <span class="keywordflow">for</span> j <span class="keywordflow">in</span> range(src_gray.shape[1]):</div><div class="line">        lambda_1 = myHarris_dst[i,j,0]</div><div class="line">        lambda_2 = myHarris_dst[i,j,1]</div><div class="line">        Mc[i,j] = lambda_1*lambda_2 - 0.04*<a class="code" href="../../d7/dcc/group__core__utils__softfloat.html#ga8bc36646a43b82baa15f151a973fb0c5">pow</a>( ( lambda_1 + lambda_2 ), 2 )</div><div class="line"></div><div class="line">myHarris_minVal, myHarris_maxVal, _, _ = <a class="code" href="../../d2/de8/group__core__array.html#ga8873b86a29c5af51cafdcee82f8150a7">cv.minMaxLoc</a>(Mc)</div><div class="line"></div><div class="line"><span class="comment"># Create Window and Trackbar</span></div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">cv.namedWindow</a>(myHarris_window)</div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">cv.createTrackbar</a>(<span class="stringliteral">&#39;Quality Level:&#39;</span>, myHarris_window, myHarris_qualityLevel, max_qualityLevel, myHarris_function)</div><div class="line">myHarris_function(myHarris_qualityLevel)</div><div class="line"></div><div class="line"><span class="comment"># My Shi-Tomasi -- Using cornerMinEigenVal</span></div><div class="line">myShiTomasi_dst = <a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga3dbce297c1feb859ee36707e1003e0a8">cv.cornerMinEigenVal</a>(src_gray, blockSize, apertureSize)</div><div class="line"></div><div class="line">myShiTomasi_minVal, myShiTomasi_maxVal, _, _ = <a class="code" href="../../d2/de8/group__core__array.html#ga8873b86a29c5af51cafdcee82f8150a7">cv.minMaxLoc</a>(myShiTomasi_dst)</div><div class="line"></div><div class="line"><span class="comment"># Create Window and Trackbar</span></div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#ga5afdf8410934fd099df85c75b2e0888b">cv.namedWindow</a>(myShiTomasi_window)</div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#gaf78d2155d30b728fc413803745b67a9b">cv.createTrackbar</a>(<span class="stringliteral">&#39;Quality Level:&#39;</span>, myShiTomasi_window, myShiTomasi_qualityLevel, max_qualityLevel, myShiTomasi_function)</div><div class="line">myShiTomasi_function(myShiTomasi_qualityLevel)</div><div class="line"></div><div class="line"><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">cv.waitKey</a>()</div></div><!-- fragment -->  </div> <h2>Explanation </h2>
<h2>Result </h2>
<div class="image">
<img src="../../My_Harris_corner_detector_Result.jpg" alt="My_Harris_corner_detector_Result.jpg"/>
</div>
<div class="image">
<img src="../../My_Shi_Tomasi_corner_detector_Result.jpg" alt="My_Shi_Tomasi_corner_detector_Result.jpg"/>
</div>
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